Re: fstrim is takes a long time on Btrfs and NVMe

Chris Murphy
2019-12-22T18:51:13Z

On Sun, Dec 22, 2019 at 11:00 AM Josef Bacik <josef@toxicpanda.com> wrote:
>
> On 12/22/19 12:49 PM, Nikolay Borisov wrote:
> > But aren't those only for inline discards e.g. when you have explicitly
> > mounted with discard. The use case here is using FITRIM ioctl, does
> > Dennis' stuff fix this?
> >
>
> I definitely misread the email, I thought he was talking about the commits being
> slow. The async discard stuff won't help with fitrim taking forever, there's
> only so much we can do in the face of shitty ssd's. Thanks,

My concern isn't this particular built-in Samsung NVMe in an HP
laptop, but whether it's sane to enable a weekly fstrim by default in
Fedora 32, via util-linux's fstrim.timer. This can't be an uncommon
situation, it's commodity name brand hardware. And opensuse and
Ubuntu, at least, have enabled this timer by default for years.

While the timer is scheduled for Monday at midnight, it's actually
likely to run during the first boot on Monday. Is it plausible there's
a setup whereby startup is blocked for the duration of this fstrim? If
so, that's way more shitty than having a shitty SSD. And if it's not
plausible, then does it matter if fstrim takes 5 minutes to run once a
week on some SSDs? I'm not seeing blocking, but what about other
shitty SSDs?

Blast from the past, this is 9 years old now: "At any rate, I
definitely think both the online trim and the FITRIM have their uses.
One thing that has burnt us in the past is coding too much for the
performance of the current crop of ssds when the next crop ends up
making our optimizations useless. This is the main reason I think the
online trim is going to be better and better. " Chris Mason
https://lwn.net/Articles/417809/

Really the industry has been schizo about this issue: totally mixed
messaging about the problem, the solution, and providing an interface
for it. In one way or another, most SSDs are shitty, depending on your
metric. Perhaps we're only just now coming out of the SSD stone age,
into the bronze age.

But what I don't want to do is make a "one size fits all" weekly timed
fstrim cause worse problems.

--
Chris Murphy